1. Field of the Invention
The present invention relates to a radio frequency identification (RFID) tag, an RFID-tag antenna, an RFID tag antenna sheet for a non-contact IC card that receives power and information from an external device and transmits information to the external device, and a method of manufacturing the RFID tag.
2. Description of the Related Art
Recently, an RFID tag (also referred to as an RFID-tag inlay, a radio IC tag, a non-contact IC tag, etc) for a non-contact integrated-circuit (IC) card that receives power and information from an external device such as a reader/writer and transmits information to the external device, without making a contact using a radio wave became popular. FIG. 18 is a plan view of a conventional RFID tag. As shown in FIG. 18, for example, an RFID tag 100 includes an antenna pattern 102 and an IC chip 103 that are provided on a film base 101 formed with a material such as plastics. The antenna pattern 102 and a capacity element embedded in the IC chip 103 form a resonant circuit. The RFID tag 100 communicates with an external device by radio through the antenna pattern 102.
The antenna pattern 102 is formed by printing a conductive ink onto the film base 101, or is formed by etching a conductor, such as a metal conductor like copper. A surface of the antenna pattern 102 and a surface of the IC chip 103 are covered with a protection film when necessary.
To improve a performance of a plane antenna of the RFID tag 100, a number of the antenna patterns 102 can be increased. FIG. 19 is a plan view of a conventional RFID tag that has a cross antenna pattern. As shown in FIG. 19, for example, the antenna pattern 102 can be formed in a cross shape. FIG. 20 is a plan view of a conventional RFID tag that has a radial antenna pattern. As shown in FIG. 20, the antenna pattern 102 can also be formed in a radial shape. The antenna pattern 102 can also be formed in a complex shape like a spiral to provide an increased area for receiving signals.
FIGS. 21 and 22 are plan views of a sheet on which a plurality of conventional RFID tags are formed. A plurality of RFID tags 100, each having the above antenna patterns 102, are formed at a same time on a same sheet 104 as shown in FIGS. 21 and 22. By cutting the sheet 104 along vertical and lateral cut lines 105, mass production of the RFID tags 100 can be achieved.
As shown in FIG. 22, each RFID tag 100 formed with the cross antenna pattern 102 occupies a large area on the sheet 104 due to a shape of the antenna pattern 102. Therefore, a production yield of the RFID tag 100 per one piece of the sheet 104 is low when cut along the cut lines 105, and as a result, manufacturing cost of the RFID tag 100 increases. This similarly applies to the RFID tag 100 that has the radial antenna pattern 102 shown in FIG. 20.
FIG. 23 is a plan view of an RFID tag antenna according to another conventional technology, and FIG. 24 is a plan view of RFID tag antennas for explaining the production yield. As shown in FIGS. 23 and 24, an RFID tag (non-contact IC card) antenna with an improved production yield of the antenna (the film base) is proposed. Such technology is disclosed in, for example, Japanese Patent Application Laid-Open No. 2001-94322.
As shown in FIG. 23, an antenna coil 180 for the RFID tag is formed as follows. A band film 110 formed in substantially a U-shape has opening ends 110a spreading toward a bottom. A conductor 120 is formed on a surface of the band film 110 spirally along a shape of the band film 110. A cut line 112 is formed at substantially a center of the band film 110 inside the conductor 120.
A band film part 114 formed inside the cut line 112 is folded at both ends of the cut line 112. The band film part 114 is folded toward a side of the open end 110a relative to a band film part 116 that is formed at a portion outside the cut line 112.
A loop band frame 150 is formed as a result. The conductor 120 is wound substantially spirally on a surface of the band film part 116a and a surface of a band film part 114 that is a surface facing an opposite side from the surface of the band film part 116, thereby forming an antenna coil 180.
Such band film 110 can improve the production yield by arranging more than one of the band film 110 on an insulation film 200 as shown in FIG. 24. In other words, a density of the band film 110 formed on the film 200 is increased by arranging in such a manner that a closed end 110b of the band film 110 is inserted without a gap from an opening end 110a of an adjacent piece of the band film 110, effectively using a portion inside the substantially U-shape of the band film 110 adjacent. With this arrangement, the formation density of the band film 110 on the film 200 is increased.
As explained with reference to FIGS. 21 and 22, when forming plane antennas, a high production yield of the RFID tag 100 cannot be obtained from the sheet 104 by simply increasing the number of antenna patterns 102. In addition, the plane antenna has a limit in improvement of reception sensitivity of a polarized wave and in directivity. Moreover, a communication distance cannot be increased.
Therefore, there is a demand for an RFID tag antenna that has an increased number of antenna patterns arranged three-dimensionally to solve the above problems. For example, it is considered possible to form a three-dimensional antenna by joining an antenna wiring perpendicularly to a surface of an antenna pattern, thereby enlarging a range of receiving a polarized wave and improving performance the antenna.
However, in many cases, a flexible film made of polyethylene telephthalate (PET) or polyimide (PI) is used for the film base of an RFID tag. Therefore, when this material is used to form a three-dimensional antenna, an increased length of the antenna increases a weight of the film base. As a result, the film base can hardly maintain a shape without flexure. When the film base becomes flexuous during use of the RFID tag, the antenna wiring also becomes flexuous, which changes a shape of the antenna. Consequently, the performance the antenna is degraded.
To avoid the flexure of the antenna wiring vertically erected, a separate reinforcing member can be provided at a root of the antenna wiring. Although stiffness of the antenna increases because of the reinforcement, manufacturing cost increases by an increase process. The provision of the reinforcing member increases mass, which may constrain an article to which the RFID tag can be applied.
According to the above conventional technique of the Japanese Patent Application Laid-Open No. 2001-94322, the formation of the antenna coil 180 can increase the production yield of the band film 110 from the film 200 as shown in FIG. 24. However, since the antenna is a plane coil antenna, there is a limit to the improvement in the reception sensitivity of a polarized wave or the improvement in directivity. Further, a communication distance cannot be increased.
Therefore, there is a demand for an RFID tag and a method of manufacturing an RFID tag that can secure a sufficiently high production yield from the material and that can improve the antenna performance. There is also a demand for an RFID tag antenna to be used for the RFID tag, and an RFID-tag antenna sheet as an aggregate of the RFID tag antennas.